Organic electroluminescent device

ABSTRACT

An organic electroluminescent device of the type which comprises an organic layer having a luminescent region and provided between an anode and a cathode, characterized in that the organic layer contains a distyryl compound represented by the following general formula:                    
     wherein R 1 , R 2 , R 3  and R 4  are a phenyl group or an aryl group of the general formula (2):                    
     and wherein R 11 , R 12 , R 13 , R 14  and R 15  may be a hydrogen atom, or at least one of them may be saturated or unsaturated alkoxyl group or an alkyl group, and R 5 , R 6 , R 7 , R 8 , R 9  and R 10  may be a cyano group, a nitro group or a halogen atom.

FIELD OF THE INVENTION

This invention relates to an organic electroluminescent device (organicEL device) wherein an organic layer having a luminescent region isprovided between an anode and a cathode.

BACKGROUND OF THE INVENTION

Lightweight, high-efficiency flat panel displays have been extensivelystudied and developed, for example, for picture display of computers andtelevision sets.

Since Cathode ray tubes (CRT) are high in luminance and exhibit goodcolor reproducibility, they are most widely employed for display atpresent. Nevertheless, the problems are involved in that the tubes arebulky, heavy and high in power consumption.

For lightweight and high efficiency flat panel displays, there have beenput on the market liquid crystal displays such as an active matrix drivetype. However, liquid crystal displays have the problems that theirangle of field is narrow, they do not rely on spontaneous light andthus, need great power consumption for back light when placed in a darkenvironment, and they do not have a sufficient response to high-speedvideo signals of high fineness which have been expected as being in usein future. Especially, it is difficult to produce a liquid crystaldisplay with a large picture size, with the attendant problem of itshigh fabrication costs.

As a substitute therefor, a display of the type using a light-emittingdiode may be possible, but such a display is also high in fabricationcosts, coupled with another problem that it is difficult to form amatrix structure of light-emitting diodes on one substrate. Thus, whenconsidered as a candidate for a low-cost display used in place ofCathode ray tubes, this type of display has a great problem to solvebefore putting to practical use.

As a flat panel display which has the possibility of solving theseproblems, attention has been recently paid to organic electroluminescentdevices (organic EL devices) using organic luminescent materials. Moreparticularly, when using organic compounds as a luminescent material, ithas been expected to realize a flat panel display, which makes use ofspontaneous light, has a high response speed and has no dependence on anangle of field.

The organic electroluminescent device is arranged that an organic thinfilm which contains a luminescent material capable of emitting lightthrough charge of an electric current and is formed between an opticallytransparent anode and a metallic cathode. In the research reportpublished in Applied Physics Letters, Vol. 51, No. 12, pp. 913 to 915(1987), C. W. Tang and S. A. VanSlyke set forth a device structure (anorganic EL device having a single hetero structure), which has adouble-layered structure including, as organic thin films, a thin filmcomposed of a hole transport material and a thin film composed of anelectron transport material and wherein luminescence occurs byre-combination of holes and electrons injected from the respectiveelectrodes into the organic films.

In this device structure, either of the hole transport material or theelectron transport material serves also as a luminescent material.Luminescence takes place in a wavelength band corresponding to theenergy gap between the ground state and the energized state of theluminescent material. When using such a double-layered structure, adrive voltage can be remarkably reduced, along with an improvedluminescent efficiency.

Thereafter, there has been developed a three-layered structure (organicEL device having a double hetero structure) of a hole transportmaterial, a luminescent material and an electron transport material asset out in the research report of C. Adachi, S. Tokita, T. Tsutsui andS. Saito, published in Japanese Journal of Applied Physics, Vol. 27, No.2, pp. L269 to L271 (1988) Moreover, a device structure comprising aluminescent material present in an electron transport material has beendeveloped as set out in the research report of C. W. Tang, S. A.VanSlyke and C. H. Chen published in Journal of Applied Physics, Vol.65, No. 9, pp. 3610 to 3616 (1989). Through these researches, evidencehas been given to the possibility of luminescence of high luminance atlow voltage, thus leading to recent, very extensive studies anddevelopments.

Organic compounds used as a luminescent material are considered to beadvantageous in that because of their diversity in kind, a luminescentcolor can be arbitrarily changed theoretically by changing theirmolecular structure. Accordingly, it may be easier on comparison withthin film EL devices using inorganic materials to provide, via propermolecular design, three colors of R (red), G (green) and B (blue) havinggood color purities necessary for full color displays.

However, organic electroluminescent devices still have problems tosolve. More particularly, a difficult is involved in the development ofa stable red luminescent device with high luminance. In an instance ofred luminescence attained by dopingDCM[4-dicyanomethylene-6-(p-dimethylaminostyryl)-2-methyl-4H-pyran] intris(8-quinolinol)aluminum (hereinafter abbreviated as Alq₃) for use asa currently reported electron transport material, this material is notsatisfactory as a display material with respect to both maximumluminance and reliability.

BSB-BCN, which was reported by T. Tsutsui and D. U. Kim in the meetingof Inorganic and Organic Electroluminescence (at Berlin, 1996), is ableto realize a luminance as high as 1000 cd/m² or over, but is not alwaysperfect with respect to the chromaticity for use as a red color for fullcolor display.

Therefore, there is a need for a red luminescent device which is high inluminance, stable and high in color purity.

In Japanese Laid-open Patent No. Hei 7-188649 (Japanese Patent No. Hei6-148798), it has been proposed to use a specific type of distyrylcompound as an organic electroluminescent material. However, theintended luminescent color is blue, not for red.

As a result, there is a need for an organic electroluminescent device,which ensures high luminance and stable red luminescence.

SUMMARY OF THE INVENTION

Intensive studies have been made in order to solve the above problem,and as a result, it has been found that when using a specific type ofdistyryl compound as a luminescent material, there can be provided ahighly reliable red luminescent device which is very useful forrealizing a stable full color display of high luminance, thus reachedcompletion of the invention.

More particularly, the invention relates to an organicelectroluminescent device of the type which comprises an organic layerwhich has a luminescent region and is provided between an anode and acathode and which contains, as an essential component, an organicmaterial capable of generating luminescence by charge of an electriccurrent, characterized in that the organic layer contains, as an organicluminescent material, at least one distyryl compound represented by thefollowing general formula (1) or the following general formula (3).

general formula (1):

provided that, in the above general formula (1), R¹, R², R³ and R⁴ are,respectively, groups which may be the same or different and represent aphenyl group or an aryl group of the following general formula (2),

general formula (2):

and provided that, in the above general formula (2), R¹¹, R¹², R¹³, R¹⁴and R¹⁵ are, respectively, groups which may be the same or different andrepresent a hydrogen atom, or at least one of them is a saturated orunsaturated alkoxyl group or an alkyl group preferably a methyl group ora tertiary butyl group, and R⁵, R⁶, R⁷, R⁸, R⁹ and R¹⁰ may be the sameor different and, respectively, represent a hydrogen atom, a cyanogroup, a nitro group or a halogen atom (including F, Cl, Br or I).

The use, as a luminescent material, of a distyryl compound representedin the above general formula (1) and/or (3) enables one not only toobtain stable red luminescence of high luminance, but also to provide adevice which has electrically, thermally or chemically good stability.The distyryl compounds of the general formula (1) or (3) may be usedsingly or in combination.

Distyryl compounds used in the organic electroluminescent device of theinvention are described.

The distyryl compound represented by the general formula (1) and used asa luminescent material in the organic electroluminescent device of theinvention may be one which has at least one of molecular structures, forexample, of the following structural formulas (4)-1, (4)-2, (4)-3,(4)-4, (4)-5, (4)-6, (4)-7, (4)-8, (4)-9 and (4)-10. These are all bis(aminostyryl) naphthyl compounds having an alkoxyphenyl group, analkylphenyl group or an unsubstituted phenyl group.

Structural formula (4)-1:

Structural formula (4)-2:

Structural formula (4)-3:

Structural formula (4)-4:

Structural formula (4)-5:

Structural formula (4)-6:

Structural formula (4)-7:

Structural formula (4)-8:

Structural formula (4)-9:

Structural formula (4)-10:

Other objects and advantages of the invention will become apparent uponreading the following detailed description and appended claims, and uponreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of an essential part of an organicelectroluminescent device according to the invention.

FIG. 2 is a schematic sectional view of another type of essential partof an organic electroluminescent device according to the invention.

FIG. 3 is a schematic sectional view of other type of essential part ofan organic electroluminescent device according to the invention.

FIG. 4 is a schematic sectional view of still other type of essentialpart of an organic electroluminescent device according to the invention.

FIG. 5 is a view showing an arrangement of a full color flat displayusing an organic electroluminescent device according to the invention.

FIG. 6 is an emission spectrogram of an organic electroluminescentdevice of Example 1 of the invention.

FIG. 7 is an emission spectrogram of an organic electroluminescentdevice of Example 2 of the invention.

FIG. 8 is an emission spectrogram of an organic electroluminescentdevice of Example 5 of the invention.

FIG. 9 is an emission spectrogram of an organic electroluminescentdevice of Example 6 of the invention.

FIG. 10 is a graph showing a voltage-luminance characteristic of anorganic electroluminescent device of Example 1 of the invention.

FIG. 11 is a graph showing a voltage-luminance characteristic of anorganic electroluminescent device of Example 2 of the invention.

FIG. 12 is a (graph showing a voltage-luminance characteristic of anorganic electroluminescent device of Example 5 of the invention.

FIG. 13 is a graph showing a voltage-luminance characteristic of anorganic electroluminescent device of Example 6 of the invention.

It should be understood that the drawings are not necessarily to scaleand that the embodiments are sometimes illustrated by graphic symbols,phantom lines, diagrammatic representations and fragmentary views. Incertain instances, details which are not necessary for an understandingof the present invention or which render other details difficult toperceive may have been omitted. It should be understood, of course, thatthe invention is not necessarily limited to the particular embodimentsillustrated herein.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIGS. 1 to 4, respectively, show examples of organic electroluminescentdevices according to the invention.

FIG. 1 shows organic electroluminescent device A of a transmission typein which luminescent light 20 passes through a cathode 3, and the light20 can also be observed from a side of a protective layer 4. FIG. 2shows organic electroluminescent device B of a reflection type whereinlight reflected at a cathode 3 can also be obtained as luminescent light20.

In the figures, numeral 1 indicates a substrate for forming an organicelectroluminescent device, which may be made of glass, plastics andother appropriate materials. Where the organic electroluminescent deviceis used in combination with other types of display devices, thesubstrate may be commonly used. Numeral 2 indicates a transparentelectrode (anode), for which ITO (indium tin oxide), SnO₂ or the likemay be used.

Numeral 5 indicates an organic luminescent layer, which contains theabove-mentioned distyryl compound as a luminescent material. For a layerarrangement for obtaining the luminescent light 20, the luminescentlayer may have hitherto known various types of layer arrangements. As isdescribed hereinafter, if a material for either a hole transport layeror an electron transport layer has luminescent properties, for example,a built-up structure of these thin films may be used. Further, in orderto increase charge transportability within a range satisfying thepurposes of the invention, either or both of a hole transport layer andan electron transport layer have a built-up structure of thin films madeof plural types of materials, or a thin film composed of a mixture ofplural types of materials may be used without limitation. In addition,in order to improve luminescent properties, at least one fluorescentmaterial may be used to provide a structure wherein a thin film of thefluorescent material is sandwiched between a hole transport layer and anelectron transport layer. Alternatively, another structure may be usedwherein at least one fluorescent is present in a hole transport layer oran electron transport layer, or in both of them. In these cases, inorder to improve a luminescent efficiency, a thin film for controllingthe transport of holes or electrons may be incorporated in a layerarrangement.

The distyryl compounds represented by the structural formula (4) haveboth electron transportability and hole transportability, and can beused as a luminescent layer serving also as an electron transport layer,or as a luminescent layer serving as a hole transport layer in thedevice arrangement. Moreover, it is possible to provide an arrangementwherein the distyryl compound is formed as a luminescent layersandwiched between an electron transport layer and a hole transportlayer.

It will be noted that in FIGS. 1 and 2, numeral 3 indicates a cathode,and an electrode material may be made of an alloy of an active metal,such as Li, Mg, Ca or the like, and a metal, such as Ag, Al, In or thelike, or a built-up structure of thin films of these metals may also beused. In the transmission-type organic electroluminescent device, anoptical transmission required for an intended application can beobtained by controlling a cathode thickness. In the figures, numeral 4indicates a sealing/protecting layer, and when an organicelectroluminescent device is wholly covered therewith, its effectincreases. Appropriate materials may be used for this provided that airtightness is ensured. Numeral 8 indicates a drive power supply forcurrent charge.

In the organic electroluminescent device of the invention, the organiclayer may have an organic built-up structure (single hetero structure)wherein a hole transport layer and an electron transport layer are builtup and wherein the above-mentioned distyryl compound is used as amaterial for forming the hole transport layer or electron transportlayer. Alternatively, the organic layer may have an organic built-upstructure (double hetero structure) wherein a hole transport layer, aluminescent layer and an electron transport layer are successively builtup, and the luminescent layer is formed of the above-mentioned distyrylcompound.

An example of an organic electroluminescent device having such anorganic built-up structure is shown. More particularly, FIG. 3 showsorganic electroluminescent device C having a single hetero structurewhich consists of a built-up structure comprising, on an opticallytransparent substrate 1, an optically transparent anode 2, an organiclayer 5 a consisting of a hole transport layer 6 and an electrontransport layer 7, and a cathode 3 superposed successively in thisorder, and the built-up structure is sealed with protective layer 4.

With such a layer arrangement as shown in FIG. 3 wherein a luminescentlayer is omitted, the luminescent light 20 with a given wavelength isemitted from the interface between the hole transport layer 6 and theelectron transport layer 7 and is observed from the side of thesubstrate 1.

FIG. 4 shows organic electroluminescent device D having a double heterostructure which consists of a built-up structure comprising, on anoptically transparent substrate 1, an optically transparent anode 2, anorganic layer 5 b consisting of a hole transport layer 10, a luminescentlayer 11 and an electron transport layer 12, and a cathode 3 superposedsuccessively in this order, the built-up structure being sealed with aprotective layer 4.

In the organic electroluminescent device shown in FIG. 4, when a DCvoltage is applied between the anode 2 and the cathode 3, the holesinjected from the anode 2 arrives at the luminescent layer 11 via thehole transport layer 10 and the electrons injected from the anode 3 alsoarrives at the luminescent layer 11 via the electron transport layer 12.Eventually, the electrons/the holes are re-combined in the luminescentlayer to generate singlet excitons, thereby causing light with a givenwavelength to be generated from the singlet excitons.

In the above-stated organic electroluminescent devices C and D,optically transparent materials such as, for example, glass, plasticsand the like may be appropriately used for the substrate 1. Where thedevices are used in combination with other types of display devices, orwhere the built-up structures shown in FIGS. 3 and 4 are located in theform of a matrix, a substrate may be commonly used. Both of the devicesC and D may have a structure of either a transmission type or areflection type.

The anode 2 consists of a transparent electrode, for which ITO (indiumtin oxide), SnO₂ or the like may be used. In order to improve a chargeinjection efficiency, a thin film made of an organic material or anorganometallic compound may be provided between the anode 2 and the holetransport layer 6 (or the hole transport layer 10). It should be notedthat where the protective layer 4 is formed of a conductive materialsuch as a metal, an insulating film may be provided at the sides of theanode 2.

The organic layer 5 a of the organic electroluminescent device Cconsists of a built-up organic layer of the hole transport layer 6 andthe electron transport layer 7, and the above-mentioned distyrylcompound may be contained in either or both of these layers to provide aluminescent hole transport layer 6 or electron transport layer 7. Theorganic layer 5 b of the organic electroluminescent device D consists ofa built-up organic layer of the hole transport layer 10, the luminescentlayer 11 containing the above-mentioned distyryl compound, and theelectron transport layer 12, and may take other various types ofbuilt-up structures. For instance, either or both of the hole transportlayer and the electron transport layer may have luminescent properties.

Especially, it is preferred that the hole transport layer 6 or electrontransport layer 7, and the luminescent layer 11, respectively, consistof a layer made of a distyryl compound used in the present invention.These layers may be formed of the above-mentioned distyryl compoundalone, or may be formed through co-deposition of the above-mentioneddistyryl compound and other type of hole or electron transport material(e.g. an aromatic amine, a pyrazoline or the like). Moreover, in orderto improve the hole transportability in the hole transport layer, a holetransport layer, which consists of a plurality of hole transportmaterials being built up, may be formed.

In the organic electroluminescent device C, the luminescent layer may bethe electron transport luminescent layer 7. In this case, light may beemitted from the hole transport layer 6 or its interface depending onthe voltage applied from a power supply 8. Likewise, in the organicelectroluminescent device D, the luminescent layer may be, aside fromthe layer 11, the electron transport layer 12 or the hole transportlayer 10. For improving the luminescent performance, it is preferred toprovide a structure wherein the luminescent layer 11 containing at leastone fluorescent material is sandwiched between the hole transport layerand the electron transport layer. Alternatively, a fluorescent materialmay be contained in the hole transport layer or the electron transportlayer, or both layers. In this connection, in order to improve theluminescent efficiency, a thin film (a hole blocking layer or anexciton-generating layer) for controlling the transport of holes orelectrons may be provided in the layer arrangement.

The materials used as the cathode 3 may be alloys of active metals suchas Li, Mg, Ca and the like and metals such as Ag, Al, In and the like,or a built-up structure of the layers of these metals may also be used.Proper selection in cathode thickness and in type of alloy enables oneto fabricate an organic electroluminescent device adapted for itsapplication.

The protective layer 4 acts as a sealing film, and is arranged to coveran organic electroluminescent device therewith as a whole, therebyensuring improved charge injection efficiency and luminescentefficiency. It should be noted that if air tightness is ensured, amaterial including a single metal such as aluminum, gold, chromium orthe like or an alloy thereof may be appropriately selected for thispurpose.

The electric current applied to the respective organicelectroluminescent devices set out hereinbefore is usually directcurrent, but pulse current or AC current may also be used. The values ofcurrent and voltage are not critical provided that they are withinranges not breaking the devices down. Nevertheless, taking into accountthe power consumption and life of the organic electroluminescentdevices, it is preferred to cause luminescence efficiently by using ofelectric energy which is as small as possible.

Next, FIG. 5 shows an arrangement of a flat display which makes use ofan organic electroluminescent device of the invention. As shown in thefigure, with the case, for example, of a full color display, organiclayers 5 (5 a, 5 b) capable of generating luminescent three primarycolors of red (R), green (G) and blue (B) are arranged between cathodes3 and anodes 2. The cathodes 3 and the anodes 2 may be provided in theform of stripe wherein they are mutually intersected, and are,respectively, applied with signal voltages, which are selected by meansof a luminance signal circuit 14 and a shift register built-in controlcircuit 15. As a result, an organic layer at a position (pictureelement) where the selected cathode 3 and anode 2 are intersected emitslight.

More particularly, FIG. 5 shows, for example, a 8×3 RGB simple matrixwherein a hole transport layer, and a built-up body 5 consisting of atleast one of a luminescent layer and an electron transport layer isprovided between the cathodes 3 and the anodes 2 (see FIG. 3 or 4). Thecathodes and anodes are patternized in the form of a stripe and aremutually intersected in a matrix, to which signal voltages are appliedin time series from the shift register built-in control circuits 15 and14, thereby causing electroluminescence or light emission at theintersected position. The EL device having such an arrangement may beused not only as a display for letters/symbols, but also as an imagereproducing apparatus. Moreover, the striped patterns of the anodes 3and the cathodes 2 are arranged for each of red (R), green (G) and blue(B) colors, thus making it possible to fabricate a solid-state flatpanel display of the multicolor or full color type.

EXAMPLES

The invention is more particularly described by way of examples, whichshould not be construed as limiting the invention thereto.

Example 1

This example illustrates fabrication of an organic electroluminescentdevice having a single hetero structure using, as a hole transportluminescent material, a compound of the following structural formula(4)-1 which is a distyryl compound of the general formula (1) wherein R²and R³, respectively, represent a 3-methoxyphenyl group, and R⁶ and R⁹,respectively, represent a cyano group.

Structural formula (4)-1:

A 30 mm×30 mm glass substrate, which had been formed with a 100 nm thickanode made of ITO on one surface thereof, was set in a vacuum depositionapparatus. A metallic mask having a plurality of 2.0 mm×2.0 mm unitopenings was placed, as a deposition mask, closely to the substrate. Thecompound of the above structural formula (4)-1 was subjected to a vacuumdeposition method at a vacuum of 10⁻⁴ Pa or below to form, for example,a 50 nm thick hole transport layer (serving also as a luminescentlayer). The deposition rate was at 0.1 nm/second.

Further, Alq₃ (tris(8-quinolinol)aluminum) of the following structuralformula was provided as an electron transport material and was depositedin contact with the hole transport layer. The electron transport layermade of Alq₃ was set at a thickness, for example, of 50 nm, and thedeposition rate was at 0.2 nm/second.

Alq₃:

A built-up film of Mg and Ag provided as a cathode material was used. Tothis end, Mg and Ag were, respectively, deposited at a deposition rateof 1 nm/second to form, for example, a 50 nm thick (Mg film) and a 150nm thick (Ag film) In this way, an organic electroluminescent device asshown in FIG. 3 was fabricated in Example 1.

Luminescent characteristics of the device were evaluated by applying aforward bias DC voltage to the thus fabricated organicelectroluminescent device of Example 1 in an atmosphere of nitrogen. Theluminescent color was red, and the device was then subjected to spectralmeasurement, with the result that, as shown in FIG. 6, spectra having aluminescent peak at 650 nm were obtained. The spectral measurement wasperformed by use of a spectroscope made by Otsuka Electronic Co., Ltd.and using a photodiode array as a detector. Moreover, when the devicewas subjected to voltage-luminance measurement, there could be obtaineda luminance of 3000 cd/m² at 8 V as is particularly shown in FIG. 10.

After the fabrication of the organic electroluminescent device, thedevice was allowed to stand over one month in an atmosphere of nitrogen,no device degradation was observed. In addition, when the device wassubjected to forced degradation wherein continuous light emission wascarried out at an initial luminance of 300 cd/m² while keeping a currentat a given level. As a consequence, it took 1500 hours before theluminance was reduced to half.

Example 2

This example illustrates fabrication of an organic electroluminescentdevice having a single hetero structure using, as an electron transportluminescent material, a compound of the structural formula (4)-1 whichis a distyryl compound of the general formula (1) wherein R¹ and R²,respectively, represent a 3-methoxyphenyl group, and R⁶ and R⁹,respectively, represent a cyano group.

A 30 mm×30 mm glass substrate, which had been formed with a 100 nm thickanode made of ITO on one surface thereof, was set in a vacuum depositionapparatus. A metallic mask having a plurality of 2.0 mm×2.0 mm unitopenings was placed, as a deposition mask, closely to the substrate.α-NPD (α-naphthylphenyldiamine) of the following structural formula wassubjected to vacuum deposition at a vacuum of 10⁻⁴ Pa or below to form,for example, a 50 nm thick hole transport layer. The deposition rate wasat 0.1 nm/second.

α-NPD:

Further, the compound of the structural formula (4)-1 used as anelectron transport material was deposited in contact with the holetransport layer. The thickness of the electron transport layer (servingalso as a luminescent layer) composed of the compound of the structuralformula (4)-1 was set, for example, at 50 nm, and the deposition ratewas at 0.2 nm/second.

A built-up film of Mg and Ag provided as a cathode material was used.More particularly, Mg and Ag were, respectively, deposited at adeposition rate of 1 nm/second to form, for example, a 50 nm thick (Mgfilm) and a 150 nm thick (Ag film). In this way, an organicelectroluminescent device of Example 2 as shown in FIG. 3 wasfabricated.

Luminescent characteristics of the device were evaluated by applying aforward bias DC voltage to the thus fabricated organicelectroluminescent device of Example 2 in an atmosphere of nitrogen. Theluminescent color was red, and the device was then subjected to spectralmeasurement as in Example 1, with the result that, as shown in FIG. 7,spectra having a luminescent peak at 650 nm were obtained. Moreover,when the device was subjected to voltage-luminance measurement, therecould be obtained a luminance of 2600 cd/rm² at 8 V as is particularlyshown in FIG. 11.

After the fabrication of the organic electroluminescent device, thedevice was allowed to stand over one month in an atmosphere of nitrogen,no degradation of the device was observed. In addition, when the devicewas subjected to forced degradation wherein continuous light emissionwas carried out at an initial luminance of 300 cd/m² while keeping acurrent at a-given level. As a consequence, it took 1200 hours beforethe luminance was reduced to half.

Example 3

This example illustrates fabrication of an organic electroluminescentdevice having a double hetero structure using, as a luminescentmaterial, a compound of the structural formula (4)-1 which is a distyrylcompound of the general formula (1) wherein R² and R³, respectively,represent a 3-methoxyphenyl group, and R⁶ and R⁹, respectively,represent a cyano group.

A 30 mm×30 mm glass substrate, which had been formed with a 100 nm thickanode made of ITO on one surface thereof, was set in a vacuum depositionapparatus. A metallic mask having a plurality of 2.0 mm×2.0 mm unitopenings was placed, as a deposition mask, near the substrate. α-NPD ofthe above-indicated structural formula was subjected to vacuumdeposition at a vacuum of 10⁻⁴ Pa or below to form, for example, a 30 nmthick hole transport layer. The deposition rate was at 0.2 nm/second.

Further, the compound of the above-indicated structural formula (4)-1used as a luminescent material was deposited in contact with the holetransport layer. The thickness of the luminescent layer composed of thecompound of the structural formula (4)-1 was set, for example, at 30 nm,and the deposition rate was at 0.2 nm/second.

Alq₃ of the above-indicated structural formula used as an electrontransport material was deposited in contact with the luminescent layer.The thickness of the Alq₃ layer was set, for example, at 30 nm, and thedeposition rate was at 0.2 nm/second.

A built-up film of Mg and Ag provided as a cathode material was used.More particularly, Mg and Ag were, respectively, deposited at adeposition rate of 1 nm/second to form, for example, a 50 nm thick (Mgfilm) and a 150 nm thick (Ag film). In this way, an organicelectroluminescent device of Example 3 as shown in FIG. 4 wasfabricated.

Luminescent characteristics of the device were evaluated by applying aforward bias DC voltage to the thus fabricated organicelectroluminescent device of Example 3 in an atmosphere of nitrogen. Theluminescent color was red, and the device was subjected to spectralmeasurement, with the result that spectra having a luminescent peak at650 nm were obtained. Moreover, when the device was subjected tovoltage-luminance measurement, there could be obtained a luminance of4000 cd/m² at 8 V.

After the fabrication of the organic electroluminescent device, thedevice was allowed to stand over one month in an atmosphere of nitrogen,no degradation of the device was observed. In addition, when the devicewas subjected to forced degradation wherein continuous light emissionwas carried out at an initial luminance of 300 cd/m² while passing acurrent at a given level. As a consequence, it took 2100 hours beforethe luminance was reduced to half.

Example 4

Example 2 was repeated with respect to the layer arrangement and thefilm formation procedures except that TPD (triphenyldiamine derivative)of the following structural formula was used as a hole transportmaterial in place of α-NPD, thereby fabricating an organicelectroluminescent device.

TPD:

The organic electroluminescent device of this example assumed redluminescence, like Example 2. The results of spectral measurement revealthat spectra were in coincidence with those of the organicelectroluminescent device of Example 2.

Example 5

This example illustrates fabrication of an organic electroluminescentdevice having a single hetero structure using, as a hole transportluminescent material, a compound of the structural formula (4)-6 whichis a distyryl compound of the general formula (3) wherein R¹⁷ and R²⁰,respectively, represent a cyano group.

Structural formula (4)-6:

A 30 mm×30 mm glass substrate, which had been formed with a 100 nm thickanode made of ITO on one surface thereof, was set in a vacuum depositionapparatus. A metallic mask having a plurality of 2.0 mm×2.0 mm unitopenings was placed, as a deposition mask, near the substrate. Thecompound of the above structural formula (4)-6 was subjected to vacuumdeposition at a vacuum of 10⁻⁴ Pa or below to form, for example, a 50 nmthick hole transport layer (serving also as a luminescent layer). Thedeposition rate was at 0.1 nm/second.

Further, Alq_(3 (tris()8-quinolinol)aluminum) of the above-indicatedstructural formula was provided as an electron transport material andwas deposited in contact with the hole transport layer. The electrontransport layer made of Alq₃ was set at a thickness, for example, of 50nm, and the deposition rate was at 0.2 nm/second.

A built-up film of Mg and Ag provided as a cathode material was used.More particularly, Mg and Ag were, respectively, deposited at adeposition rate of 1 nm/second to form, for example, a 50 nm thick (Mgfilm) and a 150 nm thick (Ag film). In this way, an organicelectroluminescent device of Example 5 as shown in FIG. 3 wasfabricated.

Luminescent characteristics of the device were evaluated by applying aforward bias DC voltage to the thus fabricated organicelectroluminescent device of Example 5 in an atmosphere of nitrogen. Theluminescent color was red, and the device was subjected to spectralmeasurement, with the result that spectra having a luminescent peak at640 nm were obtained. The spectral measurement was performed by use of aspectroscope made by Otsuka Electronic Co., Ltd. and using a photodiodearray as a detector. Moreover, when the device was subjected tovoltage-luminance measurement, there could be obtained a luminance of4000 cd/m² at 8 V as shown in FIG. 12.

After the fabrication of the organic electroluminescent device, thedevice was allowed to stand over one month in an atmosphere of nitrogen,no device degradation was observed. In addition, when the device wassubjected to forced degradation wherein continuous light emission wascarried out at an initial luminance of 300 cd/m² while passing a currentat a given level. As a consequence, it took 2000 hours before theluminance was reduced to half.

Example 6

This example illustrates fabrication of an organic electroluminescentdevice having a single hetero structure using, as an electron transportluminescent material, a compound of the structural formula (4)-6 whichis a distyryl compound of the general formula (3) wherein R¹⁷ and R²⁰,respectively, represent a cyano group.

A 30 mm×30 mm glass substrate, which had been formed with a 100 nm thickanode made of ITO on one surface thereof, was set in a vacuum depositionapparatus. A metallic mask having a plurality of 2.0 mm×2.0 mm unitopenings was placed, as a deposition mask, closely to the substrate.α-NPD (α-naphthylphenyldiamine) of the above-indicated structuralformula was subjected to vacuum deposition at a vacuum of 10⁻⁴ Pa orbelow to form, for example, a 50 nm thick hole transport layer. Thedeposition rate was at 0.1 nm/second.

Further, the compound of the structural formula (4)-6 used as anelectron transport material was deposited in contact with the holetransport layer. The thickness of the electron transport layer (servingalso as a luminescent layer) composed of the compound of the structuralformula (4)-6 was set, for example, at 50 nm, and the deposition ratewas at 0.2 nm/second.

A built-up film of Mg and Ag provided as a cathode material was used.More particularly, Mg and Ag were, respectively, deposited at adeposition rate of 1 nm/second to form, for example, a 50 nm thick (Mgfilm) and a 150 nm thick (Ag film). In this way, an organicelectroluminescent device of Example 6 as shown in FIG. 3 wasfabricated.

Luminescent characteristics of the device were evaluated by applying aforward bias DC voltage to the thus fabricated organicelectroluminescent device of Example 6 in an atmosphere of nitrogen. Theluminescent color was red, and the device was then subjected to spectralmeasurement as in example 1, with the result that, as shown in FIG. 9,spectra having a luminescent peak at 640 nm were obtained. Moreover,when the device was subjected to voltage-luminance measurement, therecould be obtained a luminance of 3500 cd/m² at 8 V as is particularlyshown in FIG. 13.

After the fabrication of the organic electroluminescent device, thedevice was allowed to stand over one month in an atmosphere of nitrogen,no degradation of the device was observed. In addition, when the devicewas subjected to forced degradation wherein continuous light emissionwas carried out at an initial luminance of 300 cd/m² while passing acurrent at a given level. As a consequence, it took 1500 hours beforethe luminance was reduced to half.

Example 7

This example illustrates fabrication of an organic electroluminescentdevice having a double hetero structure using, as a luminescentmaterial, a compound of the structural formula (4)-6 which is a distyrylcompound of the general formula (3) wherein R¹⁷ and R²⁰, respectively,represent a cyano group.

A 30 mm×30 mm glass substrate, which had been formed with a 100 nm thickanode made of ITO on one surface thereof, was set in a vacuum depositionapparatus. A metallic mask having a plurality of 2.0 mm×2.0 mm unitopenings was placed, as a deposition mask, near the substrate. α-NPD wassubjected to vacuum deposition at a vacuum of 10⁻⁴ Pa or below to form,for example, a 30 nm thick hole transport layer. The deposition rate wasat 0.2 nm/second.

Further, the compound of the above-indicated structural formula (4)-6was provided as a luminescent material and was deposited in contact withthe hole transport layer. The luminescent layer made of the compound ofthe structural formula (4)-6 was set at a thickness, for example, of 30nm, and the deposition rate was at 0.2 nm/second.

Alq₃ of the above-indicated structure formula provided as an electrontransport material was deposited in contact with the luminescent layer.The thickness of the Alq₃ was set, for example, at 30 nm, and thedeposition rate was at 0.2 nm/second.

A built-up film of Mg and Ag provided as a cathode material was used.More particularly, Mg and Ag were, respectively, deposited at adeposition rate of 1 nm/second to form, for example, a 50 nm thick (Mgfilm) and a 150 nm thick (Ag film). In this way, an organicelectroluminescent device of Example 7 as shown in FIG. 4 wasfabricated.

Luminescent characteristics of the device were evaluated by applying aforward bias DC voltage to the thus fabricated organicelectroluminescent device of Example 7 in an atmosphere of nitrogen. Theluminescent color was red, and the device was subjected to spectralmeasurement, with the result that spectra having a luminescent peak at640 nm were obtained. Moreover, when the device was subjected tovoltage-luminance measurement, there could be obtained a luminance of5200 cd/m² at 8 V.

After the fabrication of the organic electroluminescent device, thedevice was allowed to stand over one month in an atmosphere of nitrogen,no device degradation was observed. In addition, when the device wassubjected to forced degradation wherein continuous light emission wascarried out at an initial luminance of 300 cd/m² while passing a currentat a given level. As a consequence, it took 2350 hours before theluminance was reduced to half.

Example 8

Example 6 was repeated with respect to the layer arrangement and thefilm formation procedures, but TPD (triphenyldiamine derivative) wasused as a hole transport material in place of α-NPD, thereby fabricatingan organic electroluminescent device.

The organic electroluminescent device of this example assumed redluminescence, like Example 6. The results of spectral measurementrevealed that spectra were in coincidence with those of the organicelectroluminescent device of Example 6.

According to the organic electroluminescent device of the inventionwherein an organic layer having a luminescent region therein is providedbetween an anode and a cathode, the organic layer contains at least onedistyryl compound of the general formula (1) or (3), so that there canbe provided an organic electroluminescent device having high luminanceand ensuring stable red color luminescence.

From the above description it is apparent that the objects of thepresent invention have been achieved. While only certain embodimentshave been set forth, alternative embodiments and various modificationswill be apparent from the above description to those skilled in the art.These and other alternatives are considered equivalents and within thespirit and scope of the present invention.

What is claimed is:
 1. An organic electroluminescent device comprising:a cathode and an anode, an organic layer disposed between the anode andthe cathode, the organic layer comprising an organic luminescentmaterial comprising at least one distyryl compound having a generalformula (1):

wherein, R¹, R², R³ and R⁴ are selected from the group consisting of aphenyl group and an aryl group having the following general formula (2):

and wherein, R¹¹, R¹², R¹³, R¹⁴ and R¹⁵ are selected from the groupconsisting of a hydrogen atom, a saturated alkoxyl, an unsaturatedalkoxyl group, and an alkyl group, and R⁵, R⁶, R⁷, R⁸, R⁹ and R¹⁰ areselected from the group consisting of a hydrogen atom, a cyano group, anitro group and a halogen atom with the proviso that at least one of R⁵,R⁶, R⁷, R⁸, R⁹, and R¹⁰ are a cyano group, a nitro group, or a halogenatom.
 2. The organic electroluminescent device of claim 1 wherein theorganic layer comprises a hole transport layer and an electron transportlayer, and the hole transport layer comprising the distyryl compound. 3.The organic electroluminescent device of claim 1 wherein the organiclayer comprises a hole transport layer and an electron transport layer,and the electron transport layer comprising the distyryl compound. 4.The organic electroluminescent device of claim 1 wherein the organiclayer comprises a hole transport layer, a luminescent layer, and anelectron transport layer, and the luminescent layer comprising thedistyryl compound.
 5. The organic electroluminescent device comprising:a cathode and an anode, an organic layer having a luminescent region andwhich is disposed between the anode and the cathode, the organic layercomprising at least one distyryl compound selected from the groupconsisting of:


6. The organic electroluminescent device of claim 5 wherein the organiclayer comprises a hole transport layer and an electron transport layer,and the hole transport layer comprising the distyryl compound.
 7. Theorganic electroluminescent device of claim 5 wherein the organic layercomprises a hole transport layer and an electron transport layer, andthe electron transport layer comprising the distyryl compound.
 8. Theorganic electroluminescent device of claim 5 wherein the organic layercomprises a hole transport layer, a luminescent layer, and an electrontransport layer, and the luminescent layer comprising the distyrylcompound.